I find them to be too matchy for my own taste. Perhaps Arthur as a middle? That being said, if you love and agree on having brothers Luther and Arthur, then never mind what everyone else says. It's your opinion that counts!

I voted "too matchy" but I probably should have voted "other" because the problem for me is that they're too theme-y. Luther is only one letter away from Uther who was KingArthur's father in the legends. Just a heads-up- while I wouldn't do it myself, perhaps you were trying to do a theme. That being said, I love both names individually and would love the theme on a sibset whose parents were historians/classicists/etc.